How to calculate the sun protection index and know how to choose sunscreen

Sunscreens are all marked with a sun protection index. Every sunscreen has an SPF value, but the PA value may not be available. How do you calculate the sun protection index? Come and have a look.

How to calculate the sun protection index

The SPF value applies to everyone. Assuming that the intensity of ultraviolet rays does not change with time, an East Asian skin type will produce erythema after 15 minutes of sun exposure on average. According to theoretical calculations, when using SPF15 sunscreen, it means that the time can be extended by 15 times, that is, it will take 225 minutes for the skin to get sunburned; when using SPF30 sunscreen, it means that the time can be extended by 30 times, that is, it will take 450 minutes for the skin to get sunburned. The calculation method is 15 times SPF, which equals the sun protection time.

How to calculate PA value

The PA value is an index that indicates the product's ability to block long-wave UVA in sunlight. UVA damages the skin in a long-term and chronic manner, causing the skin to become tanned. The PA coefficient is represented by a "+". Generally, PA+ indicates low-efficiency protection; PA++ indicates medium-efficiency protection; and PA+++ indicates high-efficiency protection. There are also products that use UVA to indicate the sun protection factor, such as UVA12. The higher the number, the less likely you are to get tanned.

The relationship between SPF value and PA value

Preparations that absorb ultraviolet rays are divided into two types: sunscreen and tanning agents. The SPF value represents the sun protection index, which resists UVB; the PA value represents the tanning agent, which resists UVA. Using sunscreen products containing SPF values ​​can help effectively protect against the sun. If you want to protect against the sun without getting tanned, it is best to choose a sunscreen product that contains both SPF and PA factors.

What is the best sun protection factor?

If you work indoors and do not go out much, you should use sunscreen with an SPF of SPF15 to SPF20; if you need to travel outside for work or during holidays, you should use sunscreen with an SPF of SPF20 or above; if you travel to a beach or tropical area, you should use sunscreen with an SPF of SPF30 or above.